Method and system for engine water injection

ABSTRACT

Methods and systems are provided for coordinating water usage with spark usage based on the effect on an engine torque ratio. Water is injected based on torque ratio at a current spark timing relative to torque ratio at borderline knock to improve the impact of the water injection on the engine performance. Manifold water injection and direct water injected are coordinated based on intake manifold humidity.

FIELD

The present description relates generally to methods and systems forcontrolling water injection into an engine based on torque ratio.

BACKGROUND/SUMMARY

Internal combustion engines may include water injection systems thatinject water into a plurality of locations, including an intakemanifold, upstream of engine cylinders, or directly into enginecylinders. Injecting water into the engine intake air may increase fueleconomy and engine performance, as well as decrease engine emissions.When water is injected into the engine intake or cylinders, heat istransferred from the intake air and/or engine components to the water.This heat transfer leads to evaporation, which results in cooling.Injecting water into the intake air (e.g., in the intake manifold)lowers both the intake air temperature and a temperature of combustionat the engine cylinders. By cooling the intake air charge, a knocktendency may be decreased without enriching the combustion air-fuelratio. This may also allow for a higher compression ratio, advancedignition timing, and decreased exhaust temperature. As a result, fuelefficiency is increased. Additionally, greater volumetric efficiency maylead to increased torque. Furthermore, lowered combustion temperaturewith water injection may reduce NOx, while a more efficient the mixturemay reduce carbon monoxide and hydrocarbon emissions.

The cooling effect of water injection advances combustion phasing (e.g.,advances the CA50 of engine combustion). This allows fuel efficientspark timing adjustments to be made. One example of adjusting the sparktiming with the injection of water is shown by Fried et al. in U.S. Pat.No. 8,434,431. Therein, spark timing is advanced while water is injectedinto an engine. This, in turn, shifts an engine towards a higherefficiency point.

The inventors herein have recognized potential issues with the approachof '431. As one example, the approach may cause the spark timing tobounce around. For example, prior to water injection, the engine may beoperating with spark retarded by a significant amount. Then, the sparktiming may be advanced quickly responsive to the water injection.However, due to various engine operating conditions, other than thewater injection, that affect the torque, such as the octane rating ofthe injected fuel, EGR flow rate, manifold humidity, etc., the finalengine operating point with the advanced spark and the water injectionmay not be an optimum one. Consequently, to avoid knock, spark timingmay have to be retarded again. The frequent and rapid advancing andretarding of spark timing can result in an unstable torque delivery,increased NVH (noise, vibration, and harshness), and decreased fueleconomy. As a result, the full potential of the water injection is notrealized.

The inventors herein have recognized that the effect of the waterinjection on the torque ratio is not the same at all spark conditions.By continuously monitoring the torque ratio, and calibrating the waterinjection as a function of the torque ratio, spark timing adjustmentsand water injection adjustments may be better coordinated. Inparticular, the engine may be operated at the most efficient point whileusing spark and water optimally. In one example, this is achieved by amethod for an engine comprising: adjusting an amount of water injectioninto an engine responsive to a torque ratio at a current spark timingrelative to torque ratio at borderline knock, and further based onsensed humidity in an engine intake manifold.

As an example, when water injection conditions are met, a torque ratioof the current engine operating point (herein also referred to as thecurrent torque ratio) may be determined based on the current sparktiming. This torque ratio is then compared to the torque ratio of engineoperation at borderline spark (BDL) (herein also referred to as theborderline torque ratio). This includes comparing a magnitude of thedifference. In addition, a rate of change of the torque ratio (or torqueratio profile) may be determined for the given engine load condition. Ifthe current torque ratio is within a threshold distance of theborderline torque ratio (such as may occur when spark retard is between0-5 CAD of MBT), the injection of water may have a minimal effect.During such conditions, the controller may opt to conserve water andrely only on spark usage for torque control. If the torque ratio is morethan a threshold distance away from the borderline torque ratio, andfurther if the torque ratio profile indicates a rapid rate of change(such as may occur when spark retard is between 20-30 CAD of MBT), thenthe controller may infer that water injection can significantly improvethe torque ratio. During such conditions, the controller may opt toinject water at a maximum possible rate while advancing spark timing.For example, water may be injected via a manifold injector until theintake humidity of the manifold reaches a saturation limit. As a resultof the water injection, the torque ratio may be moved to a higherefficiency point. Water injection may be reduced after the torque ratiohas remained at the higher efficiency point for longer than a thresholdduration.

In this way, water injection may be better coordinated with spark usageto leverage the cooling effect of the water injection. The technicaleffect of using a monitored torque ratio to assess the efficiencyimprovement of a water injection is that spark timing may be betterplaced, and the bouncing of spark timing may be reduced. By using waterinjection based on the real-time effect of the injection on the torqueratio of an engine relative to the torque ratio at BDL, water may beused more judiciously. By limiting water injection to conditions whenthe engine efficiency improvement is significant, water may be conservedfor conditions when it is needed more. As a result, the benefits ofwater injection may be extended over a longer duration of a drive cycle.By adjusting water usage based on the torque ratio while operating theengine with one or more cylinders deactivated, engine operation in a VDEmode may be extended, improving fuel economy.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram of an engine system, including a waterinjection system.

FIG. 2 shows a flow chart of an example method for adjusting enginewater injection responsive to a torque ratio.

FIG. 3 shows a graph depicting an example change in engine torque ratiowith water injection.

FIG. 4 shows a graph depicting an example change in VDE fuel economybenefit with water injection.

FIG. 5 shows a flow chart of an example method for using water injectionto extend engine operation in a VDE mode.

FIG. 6 shows an example use of water injection based on its effect onthe torque ratio of the engine relative to BDL.

DETAILED DESCRIPTION

The following description relates to systems and methods for improvingthe usage of water from a water injection system coupled to a vehicleengine, as described with reference to the vehicle system of FIG. 1. Acontroller may be configured to perform a control routine, such as theexample routine of FIG. 2, to increase or decrease water usage based onthe torque ratio of the engine at the time of water injection relativeto the torque ratio when the engine is borderline spark limited. Thisallows the spark advancing effect of the water injection to be leveragedduring conditions when the water injection can provide a significantimprovement in torque ratio, as depicted at FIG. 3. The controller mayalso be configured to perform a control routine, such as the exampleroutine of FIG. 5, to similarly use water injection to extend engineoperation in a VDE mode based on the torque ratio effect (as depicted atFIG. 4). An example water injection adjustment is shown with referenceto FIG. 6. In this way, water usage may be improved to enablesignificant fuel economy improvements to the vehicle's performance.

FIG. 1 shows an example embodiment of an engine system 100 configuredwith a water injection system 60. Engine system 100 is coupled in motorvehicle 102, illustrated schematically. Engine system 100 includes anengine 10, depicted herein as a boosted engine coupled to a turbocharger13 including a compressor 14 driven by a turbine 116. Specifically,fresh air is introduced along intake passage 142 into engine 10 via aircleaner 31 and flows to compressor 14. The compressor may be a suitableintake-air compressor, such as a motor-driven or driveshaft drivensupercharger compressor. In the engine system 100, the compressor isshown as a turbocharger compressor mechanically coupled to turbine 116via a shaft 19, the turbine 116 driven by expanding engine exhaust. Inone embodiment, the compressor and turbine may be coupled within a twinscroll turbocharger. In another embodiment, the turbocharger may be avariable geometry turbocharger (VGT), where turbine geometry is activelyvaried as a function of engine speed and other operating conditions.

As shown in FIG. 1, compressor 14 is coupled, through charge air cooler(CAC) 118 to throttle valve (e.g., intake throttle) 20. The CAC may bean air-to-air or air-to-coolant heat exchanger, for example. Throttlevalve 20 is coupled to engine intake manifold 122. From the compressor14, the hot compressed air charge enters the inlet of the CAC 118, coolsas it travels through the CAC, and then exits to pass through thethrottle valve 20 to the intake manifold 122. In the embodiment shown inFIG. 1, the pressure of the air charge within the intake manifold issensed by manifold absolute pressure (MAP) sensor 124 and a boostpressure is sensed by boost pressure sensor 24. A compressor by-passvalve (not shown) may be coupled in series between the inlet and theoutlet of compressor 14. The compressor by-pass valve may be a normallyclosed valve configured to open under selected operating conditions torelieve excess boost pressure. For example, the compressor by-pass valvemay be opened responsive to compressor surge.

Intake manifold 122 is coupled to a series of combustion chambers orcylinders 180 through a series of intake valves (not shown) and intakerunners (e.g., intake ports) 185. As shown in FIG. 1, the intakemanifold 122 is arranged upstream of all combustion chambers 180 ofengine 10. Additional sensors, such as manifold charge temperature (MCT)sensor 33 and air charge temperature sensor (ACT) 25 may be included todetermine the temperature of intake air at the respective locations inthe intake passage. The air temperature may be further used inconjunction with an engine coolant temperature to compute the amount offuel that is delivered to the engine, for example.

Each combustion chamber may further include a knock sensor 183 foridentifying and differentiating abnormal combustion events, such asknock and pre-ignition. In alternate embodiments, one or more knocksensors 183 may be coupled to selected locations of the engine block.

The combustion chambers are further coupled to exhaust manifold 136 viaa series of exhaust valves (not shown). The combustion chambers 180 arecapped by cylinder head 182 and coupled to fuel injectors 179 (whileonly one fuel injector is shown in FIG. 1, each combustion chamberincludes a fuel injector coupled thereto). Fuel may be delivered to fuelinjector 179 by a fuel system (not shown) including a fuel tank, a fuelpump, and a fuel rail. Fuel injector 179 may be configured as a directinjector for injecting fuel directly into combustion chamber 180, or asa port injector for injecting fuel into an intake port upstream of anintake valve of the combustion chamber 180.

In the depicted embodiment, a single exhaust manifold 136 is shown.However, in other embodiments, the exhaust manifold may include aplurality of exhaust manifold sections. Configurations having aplurality of exhaust manifold sections may enable effluent fromdifferent combustion chambers to be directed to different locations inthe engine system. Universal Exhaust Gas Oxygen (UEGO) sensor 126 isshown coupled to exhaust manifold 136 upstream of turbine 116.Alternatively, a two-state exhaust gas oxygen sensor may be substitutedfor UEGO sensor 126.

As shown in FIG. 1, exhaust from the one or more exhaust manifoldsections is directed to turbine 116 to drive the turbine. When reducedturbine torque is desired, some exhaust may be directed instead througha waste gate (not shown), by-passing the turbine. The combined flow fromthe turbine and the waste gate then flows through emission controldevice 170. In general, one or more emission control devices 170 mayinclude one or more exhaust after-treatment catalysts configured tocatalytically treat the exhaust flow, and thereby reduce an amount ofone or more substances in the exhaust flow.

All or part of the treated exhaust from emission control device 170 maybe released into the atmosphere via exhaust conduit 35. Depending onoperating conditions, however, some exhaust may be diverted instead toan exhaust gas recirculation (EGR) passage 151, through EGR cooler 50and EGR valve 152, to the inlet of compressor 14. In this manner, thecompressor is configured to admit exhaust tapped from downstream ofturbine 116. The EGR valve 152 may be opened to admit a controlledamount of cooled exhaust gas to the compressor inlet for desirablecombustion and emissions-control performance. In this way, engine system100 is adapted to provide external, low-pressure (LP) EGR. The rotationof the compressor, in addition to the relatively long LP EGR flow pathin engine system 100, provides excellent homogenization of the exhaustgas into the intake air charge. Further, the disposition of EGR take-offand mixing points provides effective cooling of the exhaust gas forincreased available EGR mass and increased performance. In otherembodiments, the EGR system may be a high pressure EGR system with EGRpassage 151 connecting from upstream of the turbine 116 to downstream ofthe compressor 14. In some embodiments, the MCT sensor 33 may bepositioned to determine the manifold charge temperature, wherein thecharge may include air and exhaust recirculated through the EGR passage151.

Intake manifold 122 may further include an intake gas oxygen sensor 34.In one example, the oxygen sensor is a UEGO sensor. The intake gasoxygen sensor may be configured to provide an estimate regarding theoxygen content of fresh air received in the intake manifold. Inaddition, when EGR is flowing, a change in oxygen concentration at thesensor may be used to infer an EGR amount and used for accurate EGR flowcontrol. In the depicted example, oxygen sensor 34 is positioneddownstream of throttle 20 and downstream of charge air cooler 118.However, in alternate embodiments, the oxygen sensor may be positionedupstream of the throttle. Intake oxygen sensor 34 may be used forestimating an intake oxygen concentration and inferring an amount of EGRflow through the engine based on a change in the intake oxygenconcentration upon opening of the EGR valve 152. Likewise, intake oxygensensor 34 may be used for estimating an intake oxygen concentration andinferring an engine dilution or a change in intake humidity based on achange in the intake oxygen concentration following an intake manifoldwater injection.

Specifically, a change in the output of the sensor upon opening the EGRvalve or upon injecting water into the intake manifold is compared to areference point where the sensor is operating with no EGR or no waterinjection (the zero point). Based on the change (e.g., decrease) inoxygen amount from the time of operating with no EGR or no waterinjection, an EGR flow or water flow currently provided to the enginecan be calculated. For example, upon applying a reference voltage (Vs)to the sensor, a pumping current (Ip) is output by the sensor. Thechange in oxygen concentration may be proportional to the change inpumping current (delta Ip) output by the sensor in the presence of EGRor water relative to sensor output in the absence of EGR or water (thezero point). Based on a deviation of the estimated EGR flow from theexpected (or target) EGR flow, further EGR control may be performed.

It will be appreciated that the intake oxygen sensor 34 may be operatedin various modes based on the engine operating conditions and furtherbased on the nature of the estimation being performed by the sensor. Forexample, during engine fueling conditions when dilution/EGR estimationis required, the intake oxygen sensor may be operated in a nominal modewith a (fixed) reference voltage applied to the sensor, the referencevoltage maintained during the sensing. In one example, the referencevoltage may be 450 mV. During other conditions, such as during enginenon-fueling conditions (e.g., during a DFSO), when ambient humidity (inthe intake aircharge) estimation is required, the intake oxygen sensormay be operated in a variable voltage mode with the reference voltageapplied to the sensor modulated. In one example, the reference voltagemay be modulated between the nominal reference voltage of 450 mV and ahigher reference voltage of 800 mV (or 950 mV). By changing the intakeoxygen sensor's reference voltage, or Nernst voltage, the sensor goesfrom reacting hydrocarbons with ambient oxygen at the sensor todissociating the products of the reaction (water and carbon dioxide).Combustion chamber 180 also receives water and/or water vapor via waterinjection system 60. Water from water injection system 60 may beinjected into the engine intake or directly into the combustion chambers180 by one or more of water injectors 45-48. As one example, water maybe injected into intake manifold 122, upstream of throttle 20, via waterinjector 45, herein also referred to as central water injection. Asanother example, water may be injected into intake manifold 122,downstream of the throttle in one or more locations, via water injector46. As yet another example, water may be injected into one or moreintake runners (e.g., intake ports) 185 via water injector 48 (hereinalso referred to as port water injection), and/or directly intocombustion chamber 180 via water injector 47 (herein also referred to asdirect water injection). In one embodiment, injector 48 arranged in theintake runners may be angled toward and facing the intake valve of thecylinder which the intake runner is attached to. As a result, injector48 may inject water directly onto the intake valve, resulting in fasterevaporation of the injected water and a higher dilution benefit from thewater vapor. In another embodiment, injector 48 may be angled away fromthe intake valve and arranged to inject water against the intake airflow direction through the intake runner. As a result, more of theinjected water may be entrained into the air stream, thereby increasingthe charge cooling benefit of the water injection.

Though only one representative injector 47 and injector 48 are shown inFIG. 1, each of combustion chamber 180 and intake runner 185 may includeits own injector. In alternate embodiments, water injection system 60may include water injectors positioned at one or more of thesepositions. For example, the engine may include only water injector 46,in one embodiment. In another embodiment, the engine may include each ofwater injector 46, water injectors 48 (one at each intake runner), andwater injectors 47 (one at each combustion chamber).

Water injection system 60 may include a water storage tank 63, a waterlift pump 62, a collection system 72, and a water filling passage 69.Water stored in water tank 63 is delivered to water injectors 45-48 viawater passage 61 and conduits or lines 161. In embodiments that includemultiple injectors, water passage 61 may contain a valve 162 (e.g.,diverter valve, multi-way valve, proportioning valve, etc.) to directwater to the different water injectors via the corresponding conduits.Alternatively, each conduit (or water line) 161 may include respectivevalves within the water injectors 45-48, for adjusting water flowthere-through. In addition to water lift pump 62, one or more additionalpumps may be provided in conduits 161 for pressurizing the waterdirected to the injectors, such as in the conduit coupled to directwater injector 47.

Water storage tank 63 may include a water level sensor 65 and a watertemperature sensor 67, which may relay information regarding waterconditions to controller 12. For example, in freezing conditions, watertemperature sensor 67 detects whether the water in tank 63 is frozen oravailable for injection. In some embodiments, an engine coolant passage(not shown) may be thermally coupled with storage tank 63 to thaw frozenwater. The level of water stored in water tank 63, as identified bywater level sensor 65, may be communicated to the vehicle operatorand/or used to adjust engine operation. For example, a water gauge orindication on a vehicle instrument panel (not shown) may be used tocommunicate the level of water. If the level of water in the water tank63 is higher than a threshold level, it may be inferred that there issufficient water available for injection, and accordingly waterinjection may be enabled by the controller. Else, if the level of waterin the water tank 63 is lower than the threshold level, it may beinferred that there is insufficient water available for injection, andtherefore water injection may be disabled by the controller.

In the depicted embodiment, water storage tank 63 may be manuallyrefilled via water filling passage 69 and/or refilled automatically bythe collection system 72 via water tank filling passage 76. Collectionsystem 72 may be coupled to one or more vehicle components 74 so thatthe water storage tank can be refilled on-board the vehicle withcondensate collected from various engine or vehicle systems. In oneexample, collection system 72 may be coupled with an EGR system and/orexhaust system to collect water condensed from exhaust passing throughthe system. In another example, collection system 72 may be coupled withan air conditioning system (not shown) for collected water condensedfrom air passing through an evaporator. In yet another example,collection system 72 may be coupled with an external vehicle surface tocollect rain or atmospheric condensation. Manual filling passage 69 maybe fluidically coupled to a filter 68, which may remove some impuritiescontained in the water. A drain 92 including a drain valve 91 may beused to drain water from the water storage tank 63 to a location outsidethe vehicle (e.g., onto the road), such as when a quality of the wateris deemed to be lower than a threshold and not suitable for injectioninto the engine (e.g., due to high conductivity, high particulate mattercontent). In one example, the quality of the water may be assessed basedon the output of a sensor coupled to water injection system 60, in waterline 61. For example, the water quality may be assessed based on theoutput of a conductivity sensor, a capacitance sensor, optical sensor,turbidity sensor, density sensor, or some other type of water qualitysensor.

As discussed above, water injection may be used to provide enginedilution and charge cooling benefits, which improve engine fuel economy.In addition, when water is injected, spark timing may be advanced,increasing the engine's torque ratio and thereby moving the enginetowards a higher efficiency operating region. The inventors herein haverecognized that water injection may be used more judiciously byadjusting the water injection amount based on an expected effect of thewater injection on the torque ratio of the engine, as elaborated hereinwith reference to FIG. 2. In particular, at a given operating point(e.g., for the current engine load), the torque ratio of the engine atthe existing spark timing may be compared to the torque ratio of engineoperation at borderline spark (BDL), as discussed with reference to FIG.3. If there is a significant difference between the torque ratios, or ifthe current operating point is in a region where the torque ratio israpidly increasing with spark timing retard, the controller may inferthat water injection can be advantageously used to improve the torqueratio. Accordingly, water injection may be enabled. Else, if there is asmaller difference between the torque ratios, or if the currentoperating point is in a region where the torque ratio is not changingsignificantly with spark timing retard, the controller may infer thatwater injection will have a minimal effect on the torque ratio.Accordingly, water injection may be disabled to conserve water.

Engine system 100 may have cylinders 180 with selectively deactivatableintake valves and selectively deactivatable exhaust valves. In oneexample, the intake valves and exhaust valves are configured for camactuation via individual cam-based cylinder valve actuators. In someembodiments, engine cylinders may be grouped onto distinct engine banks.For example, where the engine 10 is a V8 engine, the engine may beconfigured with a first and a second bank, each having four cylinders.Each engine bank could then include one camshaft that actuates theintake and exhaust valves of that bank. In an alternate example, eachengine bank could include one camshaft actuating intake valves and aseparate camshaft actuating exhaust valves. In alternate examples, thevalves may be configured for electric valve actuation (EVA) via electricindividual cylinder valve actuators. Each cylinder may have a singleintake valve and a single exhaust valve, or each cylinder may have aplurality of selectively deactivatable intake valves and/or a pluralityof selectively deactivatable exhaust valves.

During selected conditions, such as when the full torque capability ofthe engine is not needed (such as when engine load is less than athreshold load, or when operator torque demand is less than a thresholddemand), one or more cylinders of engine 10 may be selected forselective deactivation (herein also referred to as individual cylinderdeactivation, or engine operation in a VDE mode). This may includeselectively deactivating one or more cylinders on only the first bank,one or more cylinders on only the second bank, or one or more cylinderson each of the first and second bank. The number and identity ofcylinders deactivated on each bank may be symmetrical or asymmetrical.

During the deactivation, selected cylinders may be deactivated byclosing the individual cylinder valve mechanisms, such as intake valvemechanisms, exhaust valve mechanisms, or a combination of both. Cylindervalves may be selectively deactivated via hydraulically actuated lifters(e.g., lifters coupled to valve pushrods), via a deactivating followermechanism in which the cam lift following portion of the follower can bedecoupled from the valve actuating portion of the follower, or viaelectrically actuated cylinder valve mechanisms coupled to eachcylinder. In addition, fuel flow and spark to the deactivated cylindersmay be stopped, such as by deactivating cylinder fuel injectors.

While the selected cylinders are disabled, the remaining enabled oractive cylinders continue to carry out combustion with fuel injectorsand cylinder valve mechanisms active and operating. To meet the torquerequirements, the engine produces the same amount of torque on theactive cylinders. This requires higher manifold pressures, resulting inlowered pumping losses and increased engine efficiency. Also, the lowereffective surface area (from only the enabled cylinders) exposed tocombustion reduces engine heat losses, improving the thermal efficiencyof the engine. Therefore, by extending operating in the VDE mode withone or more cylinders selectively deactivated, engine performance andfuel economy can be improved. As elaborated herein with reference toFIGS. 4-5, an engine controller may be able to further extend operationin the VDE mode by adjusting an amount of water injected into the enginewhile operating with the one or more cylinders deactivated based on thetorque ratio of the engine in the VDE relative to the torque ratio ofthe engine at borderline spark. In this way, spark usage and water usagecan be better coordinated to improve fuel economy.

FIG. 1 further shows a control system 28. Control system 28 may becommunicatively coupled to various components of engine system 100 tocarry out the control routines and actions described herein. Controlsystem 28 may include an electronic digital controller 12. Controller 12may be a microcomputer, including a microprocessor unit, input/outputports, an electronic storage medium for executable programs andcalibration values, random access memory, keep alive memory, and a databus. Controller 12 may receive input from a plurality of sensors 30,such as the various sensors of FIG. 1, to receive input includingtransmission gear position, accelerator pedal position, brake demand,vehicle speed, engine speed, mass airflow through the engine, boostpressure, ambient conditions (temperature, pressure, humidity), etc.Other sensors include CAC 118 sensors, such as CAC inlet airtemperature, ACT sensor 125, exhaust pressure and temperature sensors80, 82, and pressure sensor 124, CAC outlet air temperature sensor, andMCT sensor 33, intake oxygen sensor (IAO2) 34, knock sensor 183 fordetermining ignition of end gases and/or water distribution amongcylinders, and others. The controller 12 receives signals from thevarious sensors of FIG. 1 and employs the various actuators of FIG. 1 toadjust engine operation based on the received signals and instructionsstored on a memory of the controller. For example, injecting water tothe engine may include adjusting a pulse-width of injectors 45-48 tovary an amount of water injected while also adjusting a timing of thewater injection and a number of injection pulses. In some examples, thestorage medium may be programmed with computer readable datarepresenting instructions executable by the processor for performing themethods described below (e.g., at FIGS. 2 and 5) as well as othervariants that are anticipated but not specifically listed.

In this way, the system of FIG. 1 enables a vehicle system to adjust anamount of water injection into an engine responsive to a torque ratio ata current spark timing relative to torque ratio at borderline knock, andfurther based on sensed humidity in an engine intake manifold.

Turning to FIG. 2, an example method 200 is depicted for adjusting anamount of water injected into an engine responsive to an effect of thewater injection on the engine's torque ratio. Injecting water mayinclude injecting water via one or more water injectors of a waterinjection system, such as the water injection system 60 shown in FIG. 1.Instructions for carrying out method 200 and the rest of the methodsincluded herein may be executed by a controller (such as controller 12shown in FIG. 1) based on instructions stored on a memory of thecontroller and in conjunction with signals received from sensors of theengine system, such as the sensors described above with reference toFIG. 1. The controller may employ engine actuators of the engine systemto adjust engine operation, according to the methods described below.For example, the controller may send a signal to an actuator for aselected water injector to inject water at a selected location of anengine. The method coordinates water injection into an engine intakemanifold with spark usage based on a current torque ratio to providecharge cooling benefits.

The method 200 begins at 202 by estimating and/or measuring engineoperating conditions. Engine operating conditions may include drivertorque demand, manifold pressure (MAP), air-fuel ratio (A/F), currentspark timing, ambient conditions including ambient temperature,pressure, and humidity, boost pressure, an exhaust gas recirculation(EGR) rate, mass air flow (MAF), manifold charge temperature (MCT),engine speed and/or load, an engine knock level, etc.

From 202, the engine controller proceeds to perform both adaptive knockcontrol to control spark retard usage (at 204-206) and water injectioncontrol to control water usage (208-232). In addition, the spark timinginformation is used as an input to adjust the water usage so that use ofspark timing retard and water injection can be better coordinated forknock control while improving the overall fuel economy of the engine.

At 204, the method includes determining spark timing based on enginespeed and load. As such, the spark timing determined based on enginespeed and load may be a base or initial spark timing that is thenfurther adjusted to provide adaptive knock control. For example, at 202,the engine controller may refer a look-up table having engine speed andload as the input and spark timing (e.g., an amount of spark retard toapply) as the output. Alternatively, the controller may use an algorithmto make a logical determination about the spark timing based on logicrules that are a function of the engine speed and load. In one example,the base spark timing may be at MBT (or retarded from MBT by a smalleramount) at lower engine speeds and loads where knock propensity islower, and the base spark timing may be retarded from MBT (by a largeramount) at higher engine speeds and loads where knock propensity ishigher. It will be appreciated that the base spark timing is determinedbased on a feed-forward likelihood of knock, before knock is indicated.Thus, the base spark timing may be retarded further from MBT forcylinders having a higher knock propensity (e.g., cylinders having ahigher knock count, or a previous history of knock occurrence). As such,the base spark timing is selected to provide an expected knockcorrection, which corresponds to the spark angle retard applied to theoptimum ignition timing to eliminate knock. The amount of spark retardat each engine operating point is stored in the controller's memory in amap characterized by engine speed and load. The amount is then retrievedfrom the memory and reused when the engine is operated at the sameoperating point.

At 206, the method includes updating the spark timing based on sensedknock intensity and the required knock correction. That is, the basespark timing is adjusted based on feedback knock. For example,responsive to the indication of knock, spark timing may be (further)retarded from MBT. The controller may increase the degree of sparkretard applied as the sensed knock intensity increases. For example, thecontroller may use a look-up table (or an algorithm) that uses feedbackknock as an input and provides a (further) degree of spark retard to beapplied as an output. In this way, the controller may adjust the sparktiming based on each of a current engine speed and a current engineload, and further based on feedback from an engine knock sensor. Inanother example, responsive to no indication of knock, spark timing maybe gradually advanced (towards MBT). The rate of retarding sparkresponsive to sensed knock may be higher than the rate of advancingspark responsive to knock not being detected.

In addition to updating the spark timing setting based on engine speedand load, a borderline spark setting (BDL) may also be determined. BDLcorresponds to the most advanced spark setting that can be used at agiven operating condition before knocking occurs.

In parallel to performing knock adaptive spark timing control, themethod at 202 continues to 208 wherein water injection control isinitiated by determining whether water injection conditions are met.Water injection may be requested to leverage one or more benefitsassociated with water injection. For example, water injection may berequested at low-mid engine loads to increase charge dilution, therebyimproving combustion stability in the low-mid load engine operatingregion. As another example, water injection may be requested at mid-highengine loads to increase charge cooling, thereby improving knock reliefin the mid-high load engine operating region. Further still, waterinjection may be requested at high loads to provide component cooling,such as to cool the exhaust gas, cool an exhaust catalyst, etc. Waterinjection conditions may be considered met responsive to engine loadbeing higher than a threshold load (below which engine combustionstability may be affected) and spark timing being retarded (e.g., fromMBT) by more than a threshold amount.

Confirming that water injection conditions have been met may furtherinclude confirming that water is available for injection by estimatingand/or measuring water availability. Water availability for injectionmay be determined based on the output of a plurality of sensors, such asa water level sensor, a water quality sensor, and/or a water temperaturesensor disposed in the water storage tank of the water injection systemof the engine (such as water level sensor 65 and water temperaturesensor 67 shown in FIG. 1). For example, water in the water storage tankmay be unavailable for injection in freezing conditions (e.g., when thewater temperature in the tank is below a threshold level, where thethreshold level is at or near a freezing temperature). In anotherexample, the level of water in the water storage tank may be below athreshold level, where the threshold level is based on an amount ofwater required for an injection event or a period of injection cycles.

If water injection conditions are not met, at 210, the method includesdisabling water injection. In one example, where water injectionconditions are not met due to water injection not being requested, themethod includes continuing engine operation without water injection. Inanother example, where water injection conditions are not met due towater not being available for injection, such as when the water level ofthe water storage tank is below a threshold level, the controller mayindicate that refilling of the tank is required. In addition, thecontroller may refill the water tank by increasing on-board collectionof water from one or more vehicle systems, such as by collecting waterfrom a water collection system coupled to a water storage tank of awater injection system of the engine (such as water collection system 72shown in FIG. 1). This includes increasing air conditioning (AC)condenser operation to increase AC condensate collection, increasing EGRcondensate collection, increasing CAC condensate collection, etc.

However, if water injection conditions are met, at 212, the methodincludes comparing a torque ratio at the current spark timing to atorque ratio at borderline. The controller may retrieve the currentspark timing from the adaptive spark control performed at 204-206. Thetorque ratio at the current spark timing corresponds to a ratio oftorque at the current spark timing (e.g., with the determined amount ofspark retard) relative to torque at MBT timing. Likewise, the torqueratio at borderline corresponds to a ratio of torque at the current BDLsetting relative to torque at MBT timing.

As such, for a given engine operating point (e.g., a given engine load),the torque ratio changes with spark timing. In addition, various otherengine operating parameters may affect the torque ratio, such as fueloctane (or alcohol content), ambient or intake air humidity, fuel splitratio, EGR flow rate, etc. The controller may refer a map, such as theexample map of FIG. 3, to compare the final torque ratios of a givenmixture (including air, fuel, and humidity factors) at the current sparktiming relative to the BDL torque ratio. As elaborated below, comparingthe torque ratios may include comparing the torque ratio values to learnan absolute difference, or comparing the torque ratios to learn a rateof change from the torque ratio at the current spark setting to thetorque ratio at BDL. The controller may then adjust water usage based onthe comparing.

FIG. 3 depicts an example change in engine torque ratio. Map 300 depictsa first torque ratio profile at a first, lower engine load (e.g., loadof 0.1) at plot 302 (solid line) and second torque ratio profile at asecond, higher load (e.g., a load of 0.9) at plot 304 (dashed line). Asthe engine load increases, there is a corresponding increase in knocklikelihood. This results in the use of more spark timing retard whichcauses a drop in the torque ratio. In the depicted example, the torqueratio at BDL for the given engine load is depicted at point 310.

The cooling effect of water injection results in an advance incombustion phasing (that is, advanced CA50). This results in an enhancedtorque ratio. In other words, at a given load, water injection can beused to provide charge cooling, which reduces the amount of spark retardthat needs to be applied. Consequently, as water is injected, a currenttorque ratio of the engine can be moved closer to the torque ratio atBDL. As an example, by injecting water, the current torque ratio of theengine can be moved from point 306 to point 308 along torque ratioprofile 302. By comparing the position of the torque ratio at thecurrent spark timing to the torque ratio at BDL on the torque profilefor a given engine load (and fuel, humidity, and EGR combination), acontroller can determine whether to inject water or conserve water forlater use.

For example, when the engine is operating with a current spark timing ofCAD1, which is more retarded from MBT, the engine may have a currenttorque ratio depicted by point 306. The controller may determine thatthe current torque ratio is more than a threshold distance from the BDLtorque ratio depicted by point 310. The controller may furtherdetermine, based on the position of point 306 on torque profile 302,that there is a rapid rate of change in the torque ratio with an advancein the combustion phasing. That is, for every degree of spark timingadvance relative to CAD1, there is a larger increase in the currenttorque ratio, and the current torque ratio starts approaching the BDLtorque ratio faster. Therefore at this time, water injection can have alarger effect on the torque ratio and therefore a larger fuel economyand performance benefit. Accordingly when the adaptive knock controlledspark timing is determined to be CAD1, based on the comparison betweenthe torque ratio at the current spark timing (at 306) relative to thetorque ratio at borderline (at 310), the controller may determine thatwater injection should be enabled and the water injection amount shouldbe adjusted (e.g., increased).

In an alternate example, when the engine is operating with a currentspark timing of CAD2, which is less retarded from MBT, the engine mayhave a current torque ratio depicted by point 308. The controller maydetermine that the current torque ratio is less than a thresholddistance from the BDL torque ratio depicted by point 310. The controllermay further determine, based on the position of point 308 on torqueprofile 302, that there is a slow rate of change in the torque ratiowith an advance in the combustion phasing. That is, for every degree ofspark timing advance relative to CAD2, there is a smaller increase inthe current torque ratio. Therefore at this time, water injection mayhave a minimal effect on the torque ratio. Accordingly when the adaptiveknock controlled spark timing is determined to be CAD2, based on thecomparison between the torque ratio at the current spark timing (at 308)relative to the torque ratio at borderline (at 310), the controller maydetermine that water injection should be disabled and the waterinjection amount is decreased. By disabling water injection and relyingonly on spark retard for knock control at this time, water may beconserved for a later time and used only when its impact on combustionphasing advance and torque ratio is higher.

Returning to FIG. 2, at 214, the method includes determining whether thecurrent torque ratio (that is, the torque ratio at the current sparktiming) is greater than a threshold torque ratio. In one example, thethreshold torque ratio is based on the borderline torque ratio (e.g., afunction of the borderline torque ratio). The threshold torque ratio maybe set such that when the current torque ratio is higher than thethreshold torque ratio, the current torque ratio is closer to theborderline torque ratio. In an alternate example, it may be determinedif the current torque ratio is within a threshold distance of theborderline torque ratio. If the current torque ratio is within athreshold distance of the borderline torque ratio (such as may occurwhen spark retard is between 0-5 CAD of MBT), the injection of water mayhave a minimal effect, as elaborated with reference to FIG. 3. Thus, ifthe current torque ratio is greater than the threshold torque ratio, themethod continues to 216 where water is not injected for knock control.This may include maintaining water injectors disabled. Alternatively,this may include maintaining water injection at current levels (e.g.,for charge dilution purposes) and not increasing water injection toprovide knock relief. In addition, the adaptive spark timing for knockcontrol is maintained. Then, at 218, the method includes adjustingengine operation to reduce spark plug fouling. For example, spark timingretard may be maintained for a duration and/or ignition output intensitymay be increased to reduce spark plug fouling. In this way, water may beconserved for conditions when water injection would provide a greaterbenefit and spark timing is adjusted for knock control.

If the current torque ratio is not greater than the threshold torqueratio, at 220, the method includes determining, based on the torqueratio profile for the current engine load, whether a (predicted orexpected) rate of change of the torque ratio with water injection isgreater than the threshold rate. For example, with reference to FIG. 3,it may be determined if, for the given engine load, whether the torqueratio at the current spark timing is at a position on the torque ratioprofile where there is a higher than threshold rate of change in thespark timing advance direction. If the rate of change of the torqueratio with water injection is not greater than the threshold rate, suchas when the current torque ratio is in a plateau region of the torqueratio profile, it may be inferred that water usage may have a minimaleffect on the torque ratio, and therefore the method continues to 216where water is not injected.

However, if the rate of change of the torque ratio with water injectionis greater than the threshold rate, such as when the current torqueratio is in a sloped region of the torque ratio profile, at 222, themethod includes injecting water into the intake manifold. As describedabove with regard to FIG. 3, if the current torque ratio is greater thanthe threshold distance away from the borderline torque ratio and thetorque ratio profile indicates a rate of change with water injectionthat is greater than the threshold rate, the torque ratio may beimproved by water injection. Thus, at 222, the controller may enable themanifold water injector and inject water from a manifold water injector,for example at a maximum rate. The controller may send a pulse-widthsignal to the manifold injector to inject an amount of water thatprovides knock relief. Alternatively, if water injection was alreadyenabled (e.g., for dilution control), then the controller may increasewater injection for knock control. The amount of water injected may bebased on the feed-forward and feedback indication of knock. In responseto water injection, spark timing may be correspondingly advanced, andthe combustion phasing advance results in an increase in the torqueratio towards the BDL torque ratio, thereby improving engine efficiency.In this way, water may be used for knock control during conditions whenwater injection provides a greater fuel economy benefit.

Following water injection, at 224, the method includes determiningwhether the current torque ratio with water injection has been greaterthan the threshold torque ratio for a calibrated amount of time. Forexample, it may be determined if the current torque ratio with waterinjection has been at or near the borderline torque ratio for longerthan the calibrated amount of time (e.g., for a number of combustionevents, for a duration or distance of vehicle travel, etc.). If thetorque ratio is greater than the threshold for the calibrated time, itmay be inferred that continued water injection will not provide anyfurther improvement in torque ratio, and therefore at 226, the methodincludes reducing water injection. For example, manifold water injectionmay be disabled and the controller may resume only spark usage foradaptive knock control.

If the torque ratio is not greater than the threshold for the calibratedtime, at 228, the method includes estimating intake humidity. In oneexample, the intake humidity is sensed via a humidity sensor coupled tothe engine intake manifold. In another example, the intake humidity issensed via an intake oxygen sensor coupled to the engine intakemanifold. At 230, the method includes determining whether the intakehumidity is greater than a threshold. As such, manifold water injectioncan provide charge cooling benefits until a saturation limit is reached.The saturation limit may be reached when the intake manifold humidityreaches a threshold and/or when the manifold water injection reaches amaximum flow rate. If the intake humidity is greater than the threshold,the method returns to 226 wherein water injection is reduced. Thereduction in water injection may be based on the difference between thesensed intake humidity and the threshold, the water injectionpulse-width reduced further as the difference increases. Alternatively,responsive to the sensed intake humidity exceeding the threshold,manifold water injection may be disabled. In this way, the controllermay increase the amount of water injected into an intake manifold of theengine while the torque ratio at the current spark timing is below thethreshold torque ratio (or borderline torque ratio) until the sensedhumidity in the intake reaches a limit.

If intake humidity is not greater than the threshold, it may be inferredthat further water injection is possible for torque ratio improvement.Accordingly the method continues at 232 wherein the method includesdirect injecting water into one or more cylinders, if direct injectionis available, until a time or a humidity limit is reached (as describedat 224 and 230). Since water is injected at 222 into the intake manifoldat a maximum rate, and further manifold water injection is not possible,the controller employs direct injectors if the intake humidity is notabove the threshold humidity at 232. The controller may send apulse-width signal to the direct injector to inject an amount of waterdirectly into the cylinder based on a difference between the currenttorque ratio (with manifold water injection) and the borderline torqueratio. For example, as the difference increases, the pulse-width signalsent to the direct water injector may be increased. The controller maycontinue delivering water to the engine via manifold water injection (atthe maximal rate) and direct water injection to keep the torque ratioabove the threshold (e.g., close to the BDL torque ratio) until thetorque ratio remains high for longer than a threshold duration or untilthe intake humidity limit is reached. Once the time or humidity limit isreached, the method at 232 includes reducing direct water injection. Forexample, direct water injection may be disabled. Thus, after reaching asaturation limit for the manifold injection, the controller may directinject water into an engine cylinder until the torque ratio reaches thethreshold, and then disable water injection.

In this way, water injection usage may be adjusted responsive to thetorque ratio at the current spark timing relative to the torque ratio atborderline spark to improve judicious water usage. An engine controllermay adjust an amount of water injection into an engine responsive to atorque ratio at a current spark timing relative to torque ratio atborderline knock, and further based on sensed humidity in an engineintake manifold. As used herein, the torque ratio at the current sparktiming includes the torque ratio before the adjusted amount of water isinjected into the engine. The adjusting may include reducing the amountof water injected into the engine as the torque ratio at the currentspark timing approaches a threshold, the threshold based on the torqueratio at borderline knock. The method of claim 1, wherein the adjustingincludes reducing the amount of water injected into the engineresponsive to the torque ratio at the current spark timing exceeding athreshold for longer than a duration, the threshold based on the torqueratio at borderline knock. The controller may reduce the amount of waterinjected into the engine as the torque ratio at the current spark timingapproaches the torque ratio at borderline knock. The controller mayadvance spark timing from the current spark timing while injecting theadjusted amount of water.

Torque ratio comparisons can also be used to adjust water injectionduring engine operation with selective cylinder deactivation. Forexample, water may be injected to enable engine operation with selectivecylinder deactivation to be extended. The controller may compare thetorque ratio improvement (relative to borderline torque ratio) withwater injection while operating in a VDE mode with one or more cylinderdeactivated to the torque ratio improvement without water injection (andwith more spark timing retard) while operating the engine in a non-VDEmode with all cylinders active. Based on the comparison, the controllermay adjust water injection and the mode of engine operation. Aselaborated below, the controller may selectively deactivate one or moreengine cylinders responsive to the current engine load being lower thana threshold, and adjust a duration of operation with the one or morecylinders deactivated based on a torque ratio with the adjusted amountof water injected relative to torque ratio at borderline knock. Forexample, the controller may extend engine operation with the one or morecylinders deactivated when a difference between the torque ratio withthe adjusted amount of water and the torque ratio at borderline knockexceeds a threshold difference. Else, when the difference between thetorque ratio with the adjusted amount of water and the torque ratio atborderline knock is less than the threshold difference, the controllermay reactivate the one or more deactivated cylinders while disablingwater injection.

FIG. 5 shows an example method 500 for using water injection to extendengine operation in a variable displacement engine (VDE) mode. Similarto the method 200 shown in FIG. 2, in method 500, the controller mayadjust water injection based on torque ratio to extend engine operationin VDE mode.

The method 500 begins at 502 by estimating and/or measuring engineoperating conditions. Engine operating conditions estimated may includemanifold pressure (MAP), ambient conditions (ambient temperature,pressure, humidity), exhaust air-fuel ratio (A/F), exhaust gasrecirculation (EGR) flow rate, mass air flow (MAF), manifold chargetemperature (MCT), engine speed and/or load, driver torque demand,engine temperature, exhaust catalyst temperature, etc. At 504, themethod includes selecting an engine operating mode (VDE or non-VDE mode)based on engine speed and load. The controller may select VDE mode anddisable one or more engine cylinders, for example a selected group ofcylinders, such as a bank of cylinders, in response to engine speed/loadbeing lower than a threshold to increase fuel economy. As the enginespeed/load increases, the controller may switch to a non-VDE mode andreactivate previously deactivated cylinders.

Next, at 506, the method includes determining whether the engine isoperating in VDE mode. If VDE mode has not been selected, at 508, themethod includes operating the engine with all cylinders active, and withspark timing retarded from MBT by an amount based on the engine speedand average cylinder load, and further based on sensed knock intensityin the non-VDE mode. The amount of spark timing retard applied may bedetermined via adaptive spark control, as discussed earlier withreference to FIG. 2 at 204-206. In one example, the engine may beoperating with a first amount of spark timing retard when operating inthe non-VDE mode. The engine controller may refer a look-up table havingengine speed and load as the input and base/initial spark timing (e.g.,an amount of spark retard from MBT to apply) as the output. The sparktiming is then updated based on sensed knock intensity and the requiredknock correction. For example, responsive to detected knock in thenon-VDE mode, spark timing may be (further) retarded from MBT. Thecontroller may increase the degree of spark retard applied as the sensedknock intensity increases. For example, the controller may use a look-uptable (or an algorithm) that uses feedback knock as an input andprovides a (further) degree of spark retard to be applied as an output.In addition to updating the spark timing setting based on engine speedand load, a borderline spark setting (BDL) may also be determined. BDLcorresponds to the most advanced spark setting that can be used at agiven operating condition before knocking occurs. Then, the methodcontinues to 516 where the controller does not inject water. Thisincludes disabling water injectors, or maintaining the injectorsdisabled.

However, if the engine is operating in the VDE mode, at 510, the methodincludes determining spark timing retard based on engine speed andaverage cylinder load in the VDE mode, and further based on sensed knockintensity in VDE mode. As such, the average cylinder load in the VDEmode may be higher than the average cylinder load in the non-VDE mode.The amount of spark timing retard applied may be determined via adaptivespark control. In one example, the engine may be operating with asecond, different amount of spark timing retard when operating in thenon-VDE mode. The second amount of spark timing retard applied whenoperating in the non-VDE mode may be more retarded from MBT than thefirst amount of spark timing retard. The engine controller may refer alook-up table having engine speed and load as the input and base/initialspark timing (e.g., an amount of spark retard from MBT to apply) as theoutput. The spark timing is then updated based on sensed knock intensityand the required knock correction. For example, responsive to detectedknock in the VDE mode, spark timing may be (further) retarded from MBT.The controller may increase the degree of spark retard applied as thesensed knock intensity increases. For example, the controller may use alook-up table (or an algorithm) that uses feedback knock as an input andprovides a (further) degree of spark retard to be applied as an output.In addition to updating the spark timing setting based on engine speedand load, a borderline spark setting (BDL) may also be determined.

At 512, while operating in the VDE mode, the method includes comparingthe torque ratio at the current spark timing to the torque ratio at BDL.As such, for a given engine operating point (e.g., a given engine load),the torque ratio changes with spark timing. In addition, water injectionallows for combustion phasing advance, which results in an increase intorque ratio. The controller may refer a map, such as the example mapsof FIGS. 3-4, to compare the final torque ratios of a given enginemixture (including air, fuel, and humidity factors) while operating inthe VDE mode at the current spark timing relative to the BDL torqueratio. As elaborated below, comparing the torque ratios may includecomparing the torque ratio values to learn an absolute difference, orcomparing the torque ratios to learn a rate of change from the torqueratio at the current spark setting to the torque ratio at BDL. Thecontroller may then adjust water usage based on the comparing. Next, at514, the method includes determining whether the current torque ratio(that is, the torque ratio in the VDE mode with the first amount ofspark retard) is greater than a threshold torque ratio. In one example,the threshold torque ratio is based on the borderline torque ratio(e.g., a function of the borderline torque ratio). The threshold torqueratio may be set such that when the current torque ratio is higher thanthe threshold torque ratio, the current torque ratio is closer to theborderline torque ratio. In an alternate example, it may be determinedif the current torque ratio is within a threshold distance of theborderline torque ratio. If the current torque ratio is greater than thethreshold torque ratio, it may be inferred that water injection at thisoperating point has a minimal effect of the fuel economy benefit, andtherefore it may be better to conserve water and rely on spark usage forknock control. Accordingly, the method continues to 516 wherein engineoperation in the VDE mode with the first amount of spark timing retardis continued and water is not injected. This includes disabling manifoldwater injectors, or maintaining water injectors disabled.

If the current torque ratio is not greater than the threshold torqueratio, the method continues to 518 wherein the controller compares afuel economy of operating the engine with water injection enabled andcurrent spark timing more retarded in the VDE mode to operating theengine without water injection and spark timing less retarded in thenon-VDE mode.

An example of changes to a fuel economy benefit of operating in VDE modewith and without water injection is shown at map 400 of FIG. 4. In oneexample, the map of FIG. 4 may be stored in the engine controller'smemory. The controller may reference the map during engine operation tocompare the fuel economy benefit of operating in non-VDE mode toextending VDE mode operation with water injection. For example, thecontroller may determine whether to operate in the VDE mode with waterinjection by comparing the fuel economy benefit of operating in the VDEmode with and without water injection.

Map 400 shows the fuel consumption (e.g. brake specific fuelconsumption) benefit of operating in the VDE mode as a percent benefitat a given brake mean effective pressure (BMEP) with water injection (atprofile 402, solid line) and without water injection (at profile 404,dashed line). At low load conditions, the difference in the fuelconsumption benefit of VDE with water injection compared to withoutwater injection is relatively small, such as at 408 of plot 402. Incontrast, at high loads, there is a greater fuel consumption benefit ofVDE with water injection compared to without water injection at 406 ofplot 402. As engine load increases in the VDE mode, the controller maycompare the increased fuel economy of operating in VDE mode with waterinjection, shown in map 400, to the fuel economy of operating in non-VDEmode to determine whether to continue VDE operation. The cooling effectof water injection results in an advance in combustion phasing (that is,advanced CA50). This results in an enhanced torque ratio and thereby animprovement in fuel economy. In other words, at a given load whileoperating in the VDE mode, water injection can be used to provide chargecooling, which reduces the amount of spark retard that needs to beapplied for that load to provide knock control. Consequently, as wateris injected, a current torque ratio of the engine can be moved closer tothe torque ratio at BDL, as described earlier with reference to FIG. 3.Since the effect of water injection on torque ratio varies with sparktiming, and since spark timing is selected based on engine load, thefuel economy benefit of water injection during the VDE mode varies withload. For example, the fuel economy benefit at BMEP1 can be moved frompoint 405 on profile 404 to point 406 on profile 402 by injecting water.This allows operation in the VDE mode to be extended.

Further, based on the load at which water is injected, the torque ratio,and thereby the fuel economy benefit can vary. Based on the position ofthe engine operating point on profile 402, the controller can determinewhether to inject water while staying in the VDE mode or conserve waterfor later use while reactivating all cylinders and transitioning to thenon-VDE mode.

For example, when the engine is operating at BMEP1, the engine may havea fuel consumption benefit depicted by point 406. The controller maydetermine that at this operating point, there is a rapid rate of changein the fuel economy benefit with an advance in the combustion phasing.Therefore at this time, water injection can have a larger effect on thetorque ratio and therefore a larger fuel economy and performance benefitin the VDE mode. Accordingly, when the engine is at operating point 406in the VDE mode, the controller may determine that water injectionshould be enabled and the water injection amount should be adjusted(e.g., increased). This includes enabling manifold water injection. Inaddition, as water is injected, spark timing for the given load in theVDE mode can be advanced. For example, the first amount of spark timingthat was applied in the VDE mode can be reduced.

In an alternate example, when the engine is operating at BME2, theengine may have a fuel consumption benefit depicted by point 408. Thecontroller may determine that at this operating point, there is a slowerrate of change in the fuel economy benefit with an advance in thecombustion phasing. Therefore at this time, water injection may have asmaller effect on the torque ratio and therefore a smaller fuel economyand performance benefit in the VDE mode. Accordingly, when the engine isat operating point 408 in the VDE mode, the controller may determinethat water injection should be disabled.

Returning to FIG. 5, at 520, the method includes determining whether thefuel economy benefit of operating in VDE mode with water injection andspark less retarded is greater than the fuel economy benefit ofoperating in the non-VDE mode with no water injection and spark moreretarded. In one example, the controller may compare the BSFC value ofoperating in the VDE mode with water injection and spark less retardedto the BSFC value of operating in the non-VDE mode with no waterinjection and spark more retarded. The setting having the lower BSFCvalue may be selected as the setting having the higher fuel economybenefit.

If the fuel economy benefit of operating in the VDE mode is greater thanthe fuel economy benefit of operating in the non-VDE mode, the methodcontinues to 522 wherein VDE mode is maintained and water is injected atthe engine intake manifold. As a result of operating with waterinjection in the VDE mode, the engine may be operated more efficientlyat a higher torque ratio (e.g., a torque ratio that is closer to BDLtorque ratio). In this way, water injection may be used to extend VDEmode operation by providing charge cooling and associated combustionphasing advance, thereby increasing the fuel economy benefits ofoperating in the VDE mode.

Next, at 524, while operating in the VDE mode with water injectionenabled, the method includes determining whether the torque ratio isgreater than a threshold for a calibrated time. For example, it may bedetermined if the current torque ratio in the VDE mode with waterinjection has been at or near the borderline torque ratio in the VDEmode for longer than the calibrated amount of time (e.g., for a numberof combustion events, for a duration or distance of vehicle travel,etc.). If the torque ratio is not greater than the threshold for thecalibrated time, the method returns to 522. However, if the torque ratiois greater than the threshold for the calibrated time, it may beinferred that continued water injection will not provide any furtherimprovement in torque ratio and fuel economy, and therefore at 526, themethod includes disabling the VDE mode and not injecting water.Disabling the VDE mode includes reactivating all previously deactivatedcylinders and operating the engine with all cylinders active. Inaddition, spark timing may be adjusted for the non-VDE mode. Thecontroller may resume only spark usage for adaptive knock control in theno-VDE mode. For example, a larger amount of spark timing retard (e.g.,the second amount of spark retard) may be applied.

Returning to the method 520, if the fuel economy of operating in the VDEmode with water injection is lower than the fuel economy of operating inthe non-VDE mode, the method continues to 526 wherein VDE is disabledand water is not injected.

In this way, responsive to a change in engine load, a controller mayselect between operating an engine with one or more cylindersdeactivated while water is injected into an intake manifold, andoperating the engine with all cylinders active and water injectiondisabled based on a torque ratio at a current spark timing relative totorque ratio at borderline knock. The selecting may be further based onsensed humidity in the intake manifold, the humidity sensed via anintake manifold sensor. For example, the controller may select betweenoperating the engine in a VDE mode with one or more cylindersdeactivated while operating with a first spark timing or operating theengine in a non-VDE mode with all cylinders active while operating witha second, different spark timing. The controller may select the engineoperating mode based on a comparison of a first value of the torqueratio at the first spark timing relative to torque ratio at borderlineknock, and a second value of the torque ratio at the second spark timingrelative to torque ratio at borderline knock. As an example, the secondspark timing applied with all cylinders active may be more retarded thanthe first spark timing applied with one or cylinder deactivated. Theselecting may include operating the engine with the one or morecylinders deactivated and water injected into the intake manifold when afirst difference between the torque ratio at the first spark timing andthe torque ratio at borderline knock is larger than a second differencebetween the torque ratio at the second spark timing and the torque ratioat borderline knock. This allows water injection to be used to extendthe VDE mode. The controller may operate the engine with all cylindersactive and water injection disabled when the second difference is largerthan the first difference. This allows water usage to be conserved.Alternatively, the controller may operate the engine with the one ormore cylinders deactivated and water injected into the intake manifoldwhen the first difference between the torque ratio at the first sparktiming and the torque ratio at borderline knock is higher than athreshold and the second difference between the torque ratio at thesecond spark timing and the torque ratio at borderline knock is lowerthan the threshold. The controller may operate the engine with allcylinders active and water injection disabled when the first differencebetween the torque ratio at the first spark timing and the torque ratioat borderline knock is lower than the threshold and the seconddifference between the torque ratio at the second spark timing and thetorque ratio at borderline knock is higher than the threshold. Further,while operating the engine with the one or more cylinders deactivatedand water injection enabled, responsive to the torque ratio at the firstspark timing being higher than a threshold for a duration, thecontroller may reactivate the cylinders and disable the water injection,the threshold based on the torque ratio at borderline knock. Thisenables water usage to be limited when the current torque ratio hasremained elevated close to the BDL torque ratio for a duration.Furthermore, the controller may continue injecting water into the intakemanifold until the sensed humidity is at a threshold humidity, and thendisable water injection and reactivate the one or more deactivatedcylinders even if the first difference is larger than the seconddifference. This also allows water usage to be conserved when waterinjection benefits are reduced due to the presence of ambient humidity.

In FIG. 6, graph 600 illustrates example adjustments to water injectionand engine operation based on the torque ratio of the engine at a givenspark timing relative to torque ratio at borderline knock. For example,graph 600 illustrates adjustments to water injection from a manifoldwater injector or direct water injectors, and adjustments to an amountof spark timing retard that is applied as engine conditions change.Specifically, the operating parameters illustrated in graph 600 showchanges in engine load at plot 602, changes in combustion phasing(depicted as a crank angle degree at which 50% of the combustion occurs,CA50) at plot 604, changes in spark timing retard relative to MBT atplot 606, changes in torque ratio at a given spark timing (plot 608)relative to torque ratio at BDL (plot 609), an amount of water injectedvia a manifold water injector at plot 612, an amount of water injectedvia direct water injectors at plot 613, and changes in manifold relativehumidity at plot 614. For each operating parameter, time is depictedalong the horizontal axis and values of each respective operatingparameter are depicted along the vertical axis.

Prior to time t1, the engine is operating at relatively low speed and/orload conditions (plot 602). Additionally, the relative humidity is low(plot 614). At this time, no water injection is required. Also at thistime, spark timing is set to be at or around MBT (e.g., only slightlyretarded from MBT). For example, spark may be retarded such that CA50 isat 7CAD ATDC. Due to use of little to no spark retard, the engine isoperated with a high current torque ratio (e.g., torque ratio=0.99), thetorque ratio almost approaching the borderline torque ratio.

At time t1, there is an increase in engine speed/load due to an increasein torque demand. In one example, the increase in engine load is due toan operator pedal tip-in event. Due to the higher propensity for knockat the increased engine load, spark timing is retarded further from MBT.As a result, the current torque ratio (plot 608) decreases relative totorque ratio at BDL. Additionally, at time t1, the torque ratio at BDL(plot 609) decreases in response to changing engine operatingconditions. For example, torque ratio at BDL may change responsive toconditions other than spark timing, such as due to changes in EGR flow,ambient conditions, etc. As an example, spark may be retarded such thatCA50 is at 26CAD ATDC and the current torque ratio is at 0.8. Due to therelatively small difference at t1 between the current torque ratio(based on the spark timing at time t1) and the torque ratio at BDL, itmay be inferred that water injection would provide a minimal fueleconomy benefit. Consequently, the controller does not command waterinjection at t1 and instead relies only on spark retard for knockcontrol.

At time t2, the engine load (plot 602) decreases due to a decrease intorque demand. Due to the decreased engine load, the controllerdecreases spark retard (that is, advances spark timing toward MBT (plot606)). As a result, the torque ratio increases (plot 608) and CA50decreases (plot 604). Also, the current torque ratio approaches the BDLtorque ratio.

Next, at time t3, the engine load again increases due to an increase intorque demand, such as due to another operator tip-in event. Herein, theincrease in engine load is to a higher engine load than the increase att1. Based on the engine load, the adaptive spark timing amount requiredis shown at plot 607 (dashed line) with a resulting torque ratio shownat segment 610 (dashed line). In particular, a larger amount of sparkretard from MBT would be required. For example, adaptive knock controlmay require spark to be retarded from MBT such that CA50 is at 30CADATDC causing the current torque ratio to move to 0.7. If the sparktiming corresponding to plot 607 were applied, the current torque ratiowould deviate from the BDL torque ratio by a larger amount. As usedherein, the current torque ratio at the current spark timing includesthe torque ratio before an adjusted amount of water is injected into theengine. Since the torque ratio at the current spark would be greaterthan a threshold distance from the torque ratio at BDL, the controllermay infer that water injection at this engine load may provide a higherfuel economy benefit. Thus, at time t3, the controller operates with atorque ratio closer to the torque ratio at BDL by retarding spark timingand enabling manifold water injection (plot 612). Due to the waterinjection, spark timing can be advanced so that the amount of sparktiming retard applied for knock control is reduced from the level shownat plot 607 to the level shown at plot 606. This causes the combustionphasing to advance from the timing shown at plot 605 (dashed) to thetiming shown at plot 604. As an example, manifold water injection mayenable CA50 to be moved from 30CAD ATDC to 26 CAD ATDC with acorresponding change in the current torque ratio from 0.7 to 0.8 (andcloser to a BDL torque ratio of 0.99, for example). In this way, waterusage is adjusted based on the relative torque ratio to coordinate waterusage with spark usage for knock control with improved fuel economy.

As a result of the manifold water injection, relative humidity at themanifold (plot 614) increases between t3 and t4. At time t4, the engineload remains high and water injection is still required to provide knockcontrol. However, water injection from manifold injectors is at an upperlimit (plot 612). In response to manifold injection at the upper limit,to provide further knock relief, the controller additionally injectswater via direct injectors (plot 613) while maintaining the manifoldwater injection. In this way, water injection may still be usedresponsive to the relative torque ratio between the current torque ratioand the borderline torque ratio when manifold injection is at asaturation limit.

At time t5, the engine load decreases to a relatively low load due to adecrease in torque demand. Due to the decreased engine load, thecontroller decreases spark retard (that is, advances spark timing towardMBT (plot 606)) and disables water injection. As a result of the drop inspark retard usage, the torque ratio increases (plot 608) and CA50decreases (plot 604). Also, the current torque ratio approaches the BDLtorque ratio. Due to the disablement of manifold water injection, intakemanifold humidity decreases. However, the relative humidity does notdrop to levels before t3 due to an increase in the ambient humidity. Inone example, ambient humidity may increase when the vehicle is in a newlocation with higher humidity than the previous location (at t3). Inanother example, ambient humidity may increase when weather conditionschange, such as due to the presence of precipitation due to rain, fog,or snow. Due to the increased ambient humidity, BDL and torque ratio atBDL changes. At this time, the adaptive spark timing retard is small,and the current torque ratio is close to the BDL torque ratio, and sowater injection remains disabled.

At time t6, the engine load increases due to another increase in torquedemand. In one example, the relatively high engine load is due to anoperator pedal tip-in event. Additionally, ambient humidity furtherincreases. Due to a higher ambient humidity, BDL and therefore torqueratio at BDL changes again (plot 609). The controller increases sparkretard to provide knock control at the higher load (plot 606). Due tothe presence of higher relative humidity, the spark timing adjustment attime t6 moves the current torque ratio (plot 608) closer to the humidityadjusted BDL torque ratio (plot 609). Due to the smaller differencebetween the current and BDL torque ratio at this time, despite thehigher engine load and higher knock propensity, water injection is notrequired even though water injection conditions are met due to the highengine load. In particular, due to the smaller difference, it may bedetermined that water injection may not provide sufficient combustionphasing advance and sufficient improvement in torque ratio. Thereforewater is conserved for later use when water injection benefits arehigher. As elaborated above, at each engine operating point, an enginecontroller may determine a spark timing based on each of engine speed,load, and knock intensity, and compare a torque ratio at the determinedspark timing to a torque ratio at borderline knock. The controller maythen adjust an amount of water that is injected into the engine via amanifold water injector based on the comparing. The controller mayfurther adjust the amount of water that is injected based on sensedintake manifold humidity. For example, the controller may determinewhether to use spark control, water injection, or a combination thereoffor knock relief. In addition, the controller may determine whetherwater usage is optimal or not at that time for knock relief. Byadvancing the spark timing based on the adjusted amount of water, thetorque ratio of the engine can be increased and the engine can beoperated at the more fuel economical and higher performance torqueratio.

In this way, water injection parameters are adjusted based on a torqueratio at a current spark timing (without water injection adjustments)relative to the torque ratio at borderline knock. By coordinating waterinjection with spark usage, water injection may be used duringconditions when it will provide a higher benefit (per unit of waterinjected) for increased engine efficiency. The technical effect ofenabling water injection when a difference between the current torqueratio and the torque ratio at borderline knock is greater than athreshold is that use of water injection is limited to times when thewater injection has the highest impact, allowing water to be conserved.Additionally, by injecting water when a relatively large amount of sparkretard would be required to reduce knock tendency, numerous changes inspark timing with changing engine load conditions may be reduced,thereby reducing bouncing of spark timing.

As one example embodiment, a method includes adjusting an amount ofwater injection into an engine responsive to a torque ratio at a currentspark timing relative to torque ratio at borderline knock, and furtherbased on sensed humidity in an engine intake manifold. In a firstexample of the method, the method further includes wherein the torqueratio at the current spark timing includes the torque ratio before theadjusted amount of water is injected into the engine. A second exampleof the method optionally includes the first example and further includeswherein the adjusting includes reducing the amount of water injectedinto the engine as the torque ratio at the current spark timingapproaches a threshold, the threshold based on the torque ratio atborderline knock. A third example of the method optionally includes oneor more of the first and second examples, and further includes whereinthe adjusting further based on the sensed humidity includes increasingthe amount of water injected into an intake manifold of the engine whilethe torque ratio at the current spark timing is below the thresholduntil the sensed humidity in the intake reaches a limit. A fourthexample of the method optionally includes one or more of the firstthrough third examples, and further comprises, after reaching the limit,direct injecting water into an engine cylinder until the torque ratioreaches the threshold, and then disabling water injection. A fifthexample of the method optionally includes the first through fourthexamples, and further includes wherein the adjusting includes reducingthe amount of water injected into the engine responsive to the torqueratio at the current spark timing exceeding a threshold for longer thana duration, the threshold based on the torque ratio at borderline knock.A sixth example of the method optionally includes the first throughfifth examples, and further includes wherein the adjusting includesreducing the amount of water injected into the engine as the torqueratio at the current spark timing approaches the torque ratio atborderline knock. A seventh example of the method optionally includesthe first through sixth examples, and further comprises, adjusting thespark timing based on each of a current engine speed and a currentengine load, and further based on feedback from an engine knock sensor.An eighth example of the method optionally includes the first throughseventh examples, and further comprises, selectively deactivating one ormore engine cylinders responsive to the current engine load being lowerthan a threshold, and adjusting a duration of operating with the one ormore cylinders deactivated based on a torque ratio with the adjustedamount of water injected relative to torque ratio at borderline knock. Aninth example of the method optionally includes the first through eighthexamples, and further comprises wherein the adjusting includes:extending engine operation with the one or more cylinders deactivatedwhen a difference between the torque ratio with the adjusted amount ofwater and the torque ratio at borderline knock exceeds a thresholddifference; and reactivating the one or more deactivated cylinders whiledisabling water injection when difference between the torque ratio withthe adjusted amount of water and the torque ratio at borderline knock isless than the threshold difference. A tenth example of the methodoptionally includes the first through ninth examples, and furthercomprises, advancing spark timing from the current spark timing whileinjecting the adjusted amount of water.

As another example embodiment, a method comprises responsive to a changein engine load, selecting between operating an engine with one or morecylinders deactivated while water is injected into an intake manifold,and operating the engine with all cylinders active and water injectiondisabled based on a torque ratio at a current spark timing relative totorque ratio at borderline knock. In a first example of the method, themethod further includes wherein the selecting is further based on sensedhumidity in the intake manifold, the humidity sensed via an intakemanifold sensor. A second example of the method optionally includes thefirst example and further includes wherein operating the engine with oneor more cylinders deactivated includes operating with a first sparktiming, and operating the engine with all cylinders active includesoperating with a second, different spark timing, and wherein selectingbased on the torque ratio includes selecting based on a comparison ofeach of the torque ratio at the first spark timing and the torque ratioat the second spark timing to the torque ratio at borderline knock. Athird example of the method optionally includes one or more of the firstand second examples, and further includes wherein the second sparktiming is more retarded than the first spark timing. A fourth example ofthe method optionally includes the first through third examples, andfurther includes wherein the selecting includes: operating the enginewith the one or more cylinders deactivated and water injected into theintake manifold when a first difference between the torque ratio at thefirst spark timing and the torque ratio at borderline knock is largerthan a second difference between the torque ratio at the second sparktiming and the torque ratio at borderline knock; and operating theengine with all cylinders active and water injection disabled when thesecond difference is larger than the first difference. A fifth exampleof the method optionally includes one or more of the first throughfourth examples, and further comprises: while operating the engine withthe one or more cylinders deactivated and water injection enabled,responsive to the torque ratio at the first spark timing being higherthan a threshold for a duration, reactivating the cylinders anddisabling the water injection, the threshold based on the torque ratioat borderline knock. A sixth example of the method optionally includesone or more of the first through fifth examples, and further includeswherein the selecting further based on sensed humidity includesinjecting water into the intake manifold until the sensed humidity is ata threshold humidity, and then disabling water injection andreactivating the one or more deactivated cylinders even if the firstdifference is larger than the second difference.

As yet another example embodiment, a method comprises at each engineoperating point, determining a spark timing based on each of enginespeed, load, and knock intensity; comparing a torque ratio at thedetermined spark timing to a torque ratio at borderline knock; andadjusting an amount of water injected into the engine via a manifoldwater injector based on the comparing. In a first example of the method,the method further includes wherein the amount of water injected isfurther adjusted based on sensed intake manifold humidity, the methodfurther comprising advancing the spark timing based on the adjustedamount of water.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The control methods and routines disclosed herein may be stored asexecutable instructions in non-transitory memory and may be carried outby the control system including the controller in combination with thevarious sensors, actuators, and other engine hardware. The specificroutines described herein may represent one or more of any number ofprocessing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various actions,operations, and/or functions illustrated may be performed in thesequence illustrated, in parallel, or in some cases omitted. Likewise,the order of processing is not necessarily required to achieve thefeatures and advantages of the example embodiments described herein, butis provided for ease of illustration and description. One or more of theillustrated actions, operations and/or functions may be repeatedlyperformed depending on the particular strategy being used. Further, thedescribed actions, operations and/or functions may graphically representcode to be programmed into non-transitory memory of the computerreadable storage medium in the engine control system, where thedescribed actions are carried out by executing the instructions in asystem including the various engine hardware components in combinationwith the electronic controller.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and non-obvious combinationsand sub-combinations of the various systems and configurations, andother features, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

1-18. (canceled)
 19. An engine method, comprising: at each engineoperating point, determining a spark timing based on each of enginespeed, load, and knock intensity; comparing a torque ratio at thedetermined spark timing to a torque ratio at borderline knock; andadjusting an amount of water injected into an engine via a manifoldwater injector based on the comparing.
 20. The method of claim 19,wherein the amount of water injected is further adjusted based on sensedintake manifold humidity, the method further comprising advancing thespark timing based on the adjusted amount of water.
 21. The method ofclaim 19, wherein the torque ratio at the current spark timing includesthe torque ratio before the adjusted amount of water is injected intothe engine.
 22. The method of claim 19, wherein the adjusting includesreducing the amount of water injected into the engine as the torqueratio at the current spark timing approaches a threshold, the thresholdbased on the torque ratio at borderline knock.
 23. The method of claim22, further including disabling water injection and adjusting spark at athreshold.
 24. The method of claim 19, wherein the adjusting furtherbased on the sensed humidity includes increasing the amount of waterinjected into an intake manifold of the engine while the torque ratio atthe current spark timing is below the threshold until the sensedhumidity in the intake manifold reaches a limit.
 25. The method of claim19, further comprising direct injecting water into an engine cylinderuntil the torque ratio at the current spark timing reaches thethreshold, and then disabling water injection.
 26. The method of claim19, wherein the adjusting includes reducing the amount of water injectedinto the engine responsive to the torque ratio at the current sparktiming exceeding a threshold for longer than a duration, the thresholdbased on the torque ratio at borderline knock.
 27. The method of claim19, wherein the adjusting includes reducing the amount of water injectedinto the engine as the torque ratio at the current spark timingapproaches the torque ratio at borderline knock.
 28. The method of claim19, further comprising, determining the current spark timing furtherbased on feedback from an engine knock sensor.
 29. The method of claim19, further comprising adjusting an amount of water injected andsparking timing based on a determination if a variable displacement modeis active.
 30. The method of claim 29, further comprising comparing fueleconomy in an active and inactive variable displacement mode.
 31. Themethod of claim 19, further comprising, advancing spark timing from thecurrent spark timing while injecting the adjusted amount of water. 32.The method of claim 19, wherein selecting based on the torque ratioincludes selecting based on a comparison of each of the torque ratio atthe first spark timing and the torque ratio at the second spark timingto the torque ratio at borderline knock.
 33. The method of claim 19,further comprising vary an amount of water injected while also adjustinga timing of the water injection and a number of injection pulses. 34.The method of claim 19, further comprising injecting a first amount ofwater and adjusting an amount of a subsequent injection based on atorque ratio in response the first amount.
 35. The method of claim 19,further comprising comparing an amount of water to be injected to anamount of water available.
 36. The method of claim 19, furthercomprising reducing the amount of spark retardation based on an amountof water injected.
 37. The method of claim 19, wherein water is injectedinto an intake manifold, a cylinder or both.
 38. The method of claim 19,wherein a variable displacement mode duration is increased in responseto a water injection.